As its name implies, in a system which uses refrigerant as part of the heat exchange medium in a heating and cooling system, a receiver is used to hold refrigerant. Under normal operating conditions of a conventional refrigeration system which is unidirectional (i.e., is not a heat pump and does not reverse its cycle) a receiver is used to contain liquid refrigerant throughout the entire operational cycle of the system. Generally speaking, such a system operates under various operating conditions which change as a result of changes in environmental conditions. For example, if we assume that a space-cooling system begins operation when the exterior ambient temperature is 90.degree. F. and the interior temperature is 70.degree. F., a specific set of operating conditions will exist and the condensing and evaporating medium for the system will have certain mass flow requirements. If the exterior ambient then goes to 80.degree. F., the mass flow requirements which are necessary for the system to be able to perform its function in a manner which does not exceed the operating limits of the system are significantly different. Because the mass flow characteristics change from time to time, there must be a holding area for the refrigerant which is not being circulated under some conditions and that holding area is commonly a receiver.
Typically, a receiver consists of a cylindrical chamber such as chamber 10 in FIG. 1 having an inlet tube 12 connected to the top wall 13 of the chamber and an outlet dip tube 14 which extends through the top wall and terminates near the bottom wall 16 of the chamber. Liquid arriving from a condenser in the system enters through tube 12 in the top wall and, under a specific set of operating conditions, a relatively stable liquid level 15 is established within the receiver. Liquid leaves the receiver through tube 14, the lower end of which is positioned so that it is below the top of the liquid level under all normal, design operating circumstances. The size and configuration of the receiver can vary substantially, depending upon the requirements of the remainder of the system. A common rule of thumb among air conditioning engineers is that the receiver must be large enough to hold the total amount of refrigerant used in the system. Commonly, a sight glass 18 is provided so that the liquid level can be observed to establish that a sufficient quantity of refrigerant exists in the system.
Whenever a receiver of the conventional type is used in a refrigeration system, there is no concept of employing the phenomenon known as subcooling in the refrigeration system. Subcooling would be advantageous in normal refrigeration design because it assures, or approaches assuring, that the refrigerant entering the thermostatic expansion valve is a liquid which is of zero quality, meaning that there is no gas suspended in the refrigerant. However, when a liquid level is established in a receiver as illustrated at 15 in FIG. 1, there is necessarily a body of gas in the space 18 above the liquid. Any time a liquid is present with its gas, the liquid cannot be subcooled. Thus, the liquid is at a saturated temperature corresponding to the pressure of the gas above that liquid surface. FIG. 1 indicates a static condition. As the arrows indicate, liquid is entering through tube 12 and exiting through tube 14. Conventional wisdom would dictate that one not try to reverse the functions of these tubes, pumping refrigerant in through tube 14 and extracting through tube 12 because the substance extracted would be only gas unless the liquid level were to be raised to the point at which it reaches the top wall 13 of the chamber and this would be viewed as an inefficient way to operate the system. Thus, it would be completely contrary to standard practice to place a receiver in a system in a position such that refrigerant was being forced in through the dip tube 14 and caused to leave through a tube in the position of tube 12.
It has been found, however, that certain systems which are intended to operate under widely varying sets of operating conditions have system requirements which are not satisfied by the receivers of the prior art. It is highly desirable to have the receiver in the stream continuously so that it can respond to changing system requirements by adding or subtracting refrigerant from the system quickly and automatically. Efforts to provide some apparatus to accommodate the changing refrigerant requirements have involved complicated arrangements with complex control devices such as multiple solenoid valves, and have uniformly used receivers in such a way that therethrough is confined to one direction.